Focal Nodular Hyperplasia
Focal nodular hyperplasia (FNH) accounts for approximately 8% of hepatic tumors and predominantly affects young women. It represents a hyperplastic response to a vascular malformation rather than a true neoplasm. Histologically, it consists of hyperplastic hepatocytes around a malformed central artery with a fibrous stellate scar and ductular reaction. On MRI, FNH appears iso‑ to hypointense on T1‑weighted sequences and iso‑ to slightly hyperintense on T2‑weighted sequences, with a hyperintense central scar. It demonstrates strong homogeneous arterial enhancement without washout and usually shows iso‑ or hyperintensity in the hepatobiliary phase due to preserved OATP expression. These features enable highly specific diagnosis, although atypical cases with steatosis or sinusoidal dilatation may require biopsy.
Hepatocellular Adenoma
Hepatocellular adenoma (HCA) is less common but clinically significant due to its potential complications. It occurs mainly in young to middle‑aged women, often linked to oral contraceptives, obesity, or metabolic dysfunction. In men, anabolic steroid use is a key risk factor. Histologically, HCAs lack bile ducts and portal tracts. The Bordeaux classification (2017) defines several molecular subtypes: HNF1α‑inactivated adenomas (H‑HCA, approximately 30%) show diffuse steatosis and low malignant potential; inflammatory adenomas (I‑HCA, 30–35%), associated with obesity, show T2 hyperintensity with persistent contrast enhancement and may bleed; and β‑catenin‑mutated adenomas (B‑HCA) carry the highest malignant risk, particularly exon 3 mutations, which may appear iso‑ or hyperintense on the hepatobiliary contrast phase. Rare sonic hedgehog adenomas exhibit necrosis or cystic change and bleed easily.
Management
MRI with hepatobiliary contrast is essential to subtype differentiation. Not all HCAs are hypointense on the hepatobiliary phase, making them difficult to distinguish from FNH. Management depends on sex, lesion size, and subtype. Resection is advised for all adenomas in men and for women with lesions >5 cm, β‑catenin exon 3 mutations, or growth during follow‑up. Smaller adenomas may regress with hormonal withdrawal or weight loss and can be monitored.
Conclusion
FNH is a benign, nonsurgical lesion reliably diagnosed by MRI. HCA is heterogeneous with variable risks; MRI enables noninvasive differentiation and guides tailored management to prevent complications.
Competing Interests
The author has no competing interests to declare.